The goal is to elucidate the roles of proteases in the control of cellular levels of parathormone (PTH) and other secreted proteins of the parathyroid. The approach is to isolate proteases from the parathyroid and to determine if and how they cleave the peptide bonds of PTH and other proteins in vitro by chemically analyzing the cleavage products using methods of separation by chromatography, amino acid compositional analyses, and peptide sequencing. Initial experiments deal with cathepsin B and will extend to other enzymes. The cleavage products will then be compared with those hormone fragments recovered from incubation media (secreted fragments) and cell homogenates (cellular fragments) to choose the best candidates for the intracellular cleavage system. If possible, these enzymes will be initiated in situ to determine the effect on intracellular hormone metabolism and thereby test their hypothetical involvement in physiological hormone turnover.